1. Field of the Invention
The present invention relates to image capturing devices and image preprocessing methods thereof, and particularly relates to YUV format image preprocessing methods and devices.
2. Description of the Related Art
YUV encoding is a common image encoding technique in digital image processing. The YUV model defines a color space in terms of one luma component (Y) and two chrominance components (U and V). The chrominance component U, as known as Cb, shows blue-chrominance difference. The chrominance component V, as known as Cr, shows red-chrominance difference. The following shows an example of RGB-YUV transformation:Y=0.299*R+0.587*G+0.114*B, U=0.436*(B−Y)/(1−0.114), andV=0.615*(R−Y)/(1−0.299).R represents data for red color. G represents data for green color. B represents data for blue color.
Because human vision is more sensitive to variations of the luma component (Y) and less sensitive to variations of the chrominance components (U and V), chroma sub-sampling is used in YUV encoding. In chroma sub-sampling, the resolution of chroma information (U and V) is lower than that of luma information (Y). One chroma sub-sampling technique is 4:2:2 chroma sub-sampling.
FIG. 1 depicts a frame of data 100, wherein the encoding technique is 4:2:2 chroma sub-sampling. As shown, every pixel is sampled for a luma component Y, and every two pixels share a chrominance component U and a chrominance component V. For example, pixel 102, in row 0 and column 0, provides a luma component Y00 and a blue-chrominance difference U00 but not a red-chrominance difference (V), and pixel 104 in row 0 and column 1 provides a luma component Y01 and a red-chrominance difference V01 but not a blue-chrominance difference (U). Pixels 102 and 104 share the blue-chrominance difference U00 and red-chrominance difference V01.
A digital image may be compressed to data stream. Before being compressed, the image is typically divided into a plurality of sub-images to be sequentially compressed. To collect data for one sub-image, conventional techniques may use line buffers.
The line buffers, furthermore, may be used in other applications. For example, the digital image may be buffered by the line buffers before being displayed.
It is an important issue for a person skilled in the art to reduce the number of the line buffers.